The present invention is directed to a method of and mold for the aluminothermic welding of rails. Rails to be aluminothermically welded are enclosed in a sand mold so that the mold extends over the adjoining rail ends and encloses the space between the ends. The sand mold is formed of silica sand. The aluminothermic reaction takes place in a crucible located above the mold and superheated molten metal from the reaction is tapped into the space between the rail ends.
At the present time, in the railroad industry extensive maintenance and repair of the track is required. As a part of the maintenance program, worn or damaged rails are removed and replaced with new rails. To provide a continuous surface, the new rails are joined to existing rails by welding to form a surface affording a smoother ride and greatly reducing the battering of the rail ends which occurs when the ends are connected together by joint bars. Other types of rail, such as crane rails, are also welded together.
In the past, several methods including aluminothermic welding have been used for welding rails in the field. Aluminothermic welding is used extensively because of its general simplicity and low cost. The equipment required is inexpensive, it is readily portable to remote areas, and workers can be trained in a relatively short time to make satisfactory aluminothermic welds.
In preparation for aluminothermic welding, rail ends are aligned and separated by a gap of approximately one inch. A silica sand mold is placed around the rail ends and encloses the gap. Initially, the rail ends are preheated with a burner. Subsequently, the aluminothermic material is ignited in the crucible located above the mold and the superheated weld metal is tapped into the gap between the rail ends to form the weld. After a relatively short time, the sand mold is removed and excess weld metal is sheared and ground off leaving the weld metal joint ready for use.
One of the problems experienced with aluminothermic welds is that the weld metal has about twice the superheat of normal molten steel during teeming and, as a result, attacks the surfaces of the mold in direct contact with the rail ends. Due to the superheat, pockmarks and other surface defects are formed in the sides or collar of the weld metal. Any visible imperfections in the weld collar cause concern about the general quality of the weld and/or its subsequent fatigue life. It has been standard practice with some railway companies that the collar defects and/or the entire collar are removed by hand-held grinding tools. Manual grinding of the aluminothermic weld collars is tedious, costly and time consuming.